Trend Micro's complaint that Microsoft is cutting corners by delivering antivirus signatures and patches via Windows Update rather than an updater built into its antivirus product, as other vendors do, is just one indication that the whole antivirus market is about to go through an upheaval and probably consolidation as well.

Not only is Microsoft Security Essentials one of the best-reviewed products even among free and open-source options -- an accomplishment in itself -- its price of $0 has helped accelerate changes that would be caused by changes in technology anyway.

Sophos, for example, offers its antivirus free for Macintosh users. Most of the big AV vendors also offer free scans online -- though these are more of a come-on to buy the commercial version than a real service even for those that will clean all the viruses it finds, rather than offering possibly bogus warnings and a hard-sell for the premium edition.

Forty-four percent of consumers with smartphones or other intelligent mobile devices use them for work as well as personal tasks; of those, 81 percent do it without permission from IT, according to a study from Juniper Networks. That means a huge chunk of IT endpoints are vulnerable, a rush among antivirus vendors to cover them, and consolidation such as Intel's acquisition of McAfee driven by non-security companies who also see cleaning the endpoints as a requirement for any mobile product.

Companies such as AV-Comparatives, Portcullis Security and others build server-based appliances customers can plug into their networks to, among other things, let companies that can't afford their own security specialists to hire outside services to handle that for them.

Cloud-based startups, however -- some free, some paid, some still in beta and not yet free or paid -- could quickly change both the economics and practice of the whole market.

Euro-brand Panda Security has set up a cloud-service offering from new facilities in California, from which it plans to take advantage of the U.S. part of a global market that has grown for Panda at 65 percent over the past year and will grow from 15 percent of total revenue to 20 percent by the end of next year, according to projections in Panda's release.

Pure-play Web services such as ipTrust, from startup Endgame Systems, emphasizes the availability and scale of a cloud-based service mixed with "petabyte-scale data processing" of information about botnets, virii and other threats. ipTrust is still in beta, so no price is set, but other cloud antivirus services such as Immunet offer free options and often very low costs. Even the more commercial, business-oriented Panda's cloud goes for 29 Euros per seat, setting a pretty low bar for potential competitors.

Either way, there is a big market at stake, and a constituency of end-user companies perpetually dissatisfied with whichever antivirus vendor they use. As the impact of cloud providers increases, so does the potential instability of the market and the potential for free to unseat paid and consolidation to change the list of providers even enterprise customers can choose among.